Gas turbines are widely used in commercial operations for power generation. A conventional gas turbine includes a plurality of combustors disposed around an annular array about the axis of the engine. A compressor supplies compressed air to each combustor, wherein the compressed air and fuel are mixed and burned. Hot gases of combustion flow from each combustor to the turbine section of the engine wherein energy is extracted from the combustion gases to produce work.
It is widely known that the thermodynamic efficiency of a gas turbine increases as the operating temperature, namely the combustion gas temperature, increases. Higher temperature combustion gases contain more energy and produce more work as the combustion gases expand in the turbine. However, as temperatures have been increased to improve the efficiency of gas turbines, it has become necessary to provide cooling air to the turbine components in order to maintain the temperatures of such components at acceptable levels. Thus, at higher operating condition temperatures, the amount of cooling air that is required is relatively high. In contrast, during lower temperature operating conditions, less cooling air is required for certain turbine components. Moreover, the amount of cooling required can vary from engine-to-engine, for example, due to first stage bucket leakage, hot gas ingestion, or surrounding environmental conditions.
In spite of these differing operating conditions and engine-to-engine variations, the prior art has not generally provided a system that modulates the flow of air delivered to the turbine components. As a result, since the engine must be designed to provide for maximum temperature operation, an excessive amount of cooling air is provided during lower temperature operation, which tends to reduce the efficiency of the engine during such operating periods.
Accordingly, there is a need for a system in a gas turbine that provides cooling air to turbine components only as needed, for example during higher temperature operation. Such a system would lead to improved efficiency and increased output during lower temperature operation without compromising turbine components during higher temperature operation.